The present invention relates to a method of making a memory card that is capable, without electrical contact, of exchanging information with a reader device.
A particularly advantageous application of the invention is in the field of manufacturing contactless cards, in particular those used as travel tickets or as badges for access to protected premises.
In very general terms, information is exchanged between a contactless card and the reader device with which it is associated by remote electromagnetic coupling between a first antenna housed in the body of the contactless card and a second antenna situated in the reader device. The card is also provided with a semiconductor die, or chip, connected to the first antenna and containing, among other things, both a memory in which the information to be provided to the reader device is stored, and means, e.g. a microprocessor, provided to generate the information that is to be transmitted and to process the information that is received.
The contactless cards that are currently in existence are constituted by an electronic circuit in the form of an insert which is usually embedded in a card body made of a plastics material. The insert includes the antenna for coupling the card, the semiconductor die, and an interconnection circuit for interconnecting the antenna and the die. The semiconductor die is generally mounted on the interconnection circuit using a wire bonding technique which consists of connecting the input/output metallizations of the semiconductor die by means of gold wires for example, to the contact areas disposed on the interconnection circuit, and to which there are connected the electrical connection terminals of the coupling antenna. In order to protect the semiconductor die and the connection wires, the assembly is embedded in an insulating resin. The semiconductor die mounted in this way on the interconnection circuit is called an xe2x80x9celectronic modulexe2x80x9d.
The antenna itself is made either from wound enamelled wire that is connected to the contact areas of the interconnection circuit, or by means of a printed or etched circuit connected to the interconnection circuit.
The techniques known for making contactless cards that implement an electronic module present the following drawbacks:
(a) The electronic module has to be made beforehand.
(b) The modules are thick because of the loops formed by the connection wires. In addition, the thickness is further increased by the protective molding which is also very costly to make.
(c) Because of the total thickness of the connected and protected semiconductor die, it is difficult, especially if a defect-free surface of the card is to be guaranteed, to mount the electronic module directly on the printed or etched circuit carrying the coupling antenna and to keep the thickness of the card to the ISO standard (760 xcexcm). This last point is all the more critical as plasticization makes it necessary to place the antenna close to the middle of the card and to keep the structures symmetrical in order to prevent the card from bending. For this reason, the module is mounted through the antenna circuit so as to balance the volume of plastics material on each side of the antenna, thereby imposing an additional operation of piercing the printed or etched circuit.
(d) The wound antenna insert is very difficult to plasticize while guaranteeing a good plane surface, and plasticization can only be performed on a unit by unit basis.
(e) For both types of inserts (i.e. with wound antenna and with printed or etched antenna circuit), the dimensions of the module in the plane of the card are very large, generally giving rise to flatness defects in the finished card at the bottom of the module over areas that are also large.
Published European patent application number EP-A3-0 706 152 describes a method of manufacturing a chip card in which the flip-chip technique is used to provide a chip on conductive tracks, e.g. tracks printed on the surface of a thermoplastics film. In that method, each of the intermediate sheets, designed to be superposed on the surface of the thermoplastics film carrying the conductive tracks, has a cutout forming an opening in which the chip is received during a laminating step.
However, in such a method, the opening made in the intermediate sheets must be accurately sized to conform to the dimensions of the chip. In other words, the openings made in the intermediate sheet(s) must be accurately superposed, and the clean edges of the cavity thus formed must be disposed as close as possible to the edges of the chip. Otherwise, temperature differences, or indeed creep of the material, can give rise to deformations on the surface of the card, with such deformations generally resulting in the graphics printed on the surface being spoiled.
It is also noted that injecting resin around the chip, which could enable the space between the chip and the edges of the cavity to be filled, is not easy to achieve given the small size of the space compared with the size of the chip; it is much smaller than that of a micro-module. In addition, such injection would consequently result in increasing the cost of manufacturing the cards.
One object of the present invention is to provide an improved electronic memory card that is capable, without electrical contact, of exchanging information with a reader device, the electronic memory card including a coupling antenna for coupling with the reader device, and a semiconductor die connected to the antenna.
Another object of the present invention is to reduce the overall size of the semiconductor die.
A further object of the present invention is to improve the operation of connecting the die to the coupling antenna.
Yet another object of the present invention is to enable the drawbacks relating to openings formed in the intermediate sheet(s) to be avoided.
These and other objects are attained in accordance with one aspect of the present invention which includes, on a support sheet of plastics material, a coupling antenna provided with two electrical connection terminals. A semiconductor die having protruding contacts is mounted on said electrical connection terminals. An intermediate sheet made of plastics material that is designed to cover said semiconductor die is placed on the support sheet thus equipped and constituting said electronic circuit. An outer sheet made of plastics material is placed at least on said intermediate sheet. The set of said sheets is laminated together by the application of heat and pressure.
By implementing the xe2x80x9cflip-chipxe2x80x9d technique, the semiconductor die is connected to the coupling antenna in a single operation without passing via a connection circuit. Because of the absence of connection wires and of protective embedding, the die remains thin, and its side dimensions remain small (2 mm instead of 15 mm for an electronic module).
In addition, the support sheet carrying the coupling antenna does not need to be cut to prepare an opening for receiving the semiconductor die. Thus, the invention has the advantage of avoiding making an opening in the intermediate sheet. The inventor has been able to establish that, after lamination and because of its small size, the semiconductor die does not produce a noticeable extra thickness in the surface of the outer sheet which lies over the die.
It should also be pointed out that the contactless electronic card of the invention can be made by various production techniques, such as card by card, or in continuous slabs or strips, and the sheets may be of any size.